Cowry/cowrie. They're basically weird snails... touch its mantle and get it to retract so you can photograph the shell, then someone can get you a specific ID.
I think it's a money cowrie. Can't be certain without a shell picture, but it looks like mine. They're good because they eat algae pretty well, plus they're unique. Also, hermit crabs have a hard time reaching into the shell to kill them, like they'll do with snails.